The present invention relates to a sawing apparatus for cutting a cant along a curve. More particularly, it relates to a sawing apparatus which senses the curvature of a cant along a smooth (or sawn) side of the cant and adjusts the saw head by raising or lowering the saw head so as to cut a board of a preset thickness, following the curvature of the cant.
In prior art cant cutting saws, such as that described in Kenyon (U.S. Pat. No. 4,127,044), the vertically oriented saw head remains stationary (is not moved up or down or sideways) while the cant is displaced horizontally so that the cant may be cut following the curvature of the cant. A sensing roller 25 (also referred to as a surface locator) senses the curvature on the wany side of the cant (not the smooth, sawn side), and an orienting pressure roller 6 pushes on the cant based on the feedback from the sensing roller 25, thus guiding the cant through the saw head so as to cut the cant while following its curvature. A control pressure roller 13 offers a degree of resistance to the force exerted on the cant by the orienting pressure roller 6.
In Kenyon, the cant is oriented with its curvature on the side instead of on the bottom. However, the smooth (sawn) sides of the cant are on top and on the bottom of the cant. Therefore, the sensing of the curvature is done on the wany side of the cant, which is rough, having bumps and other irregularities that are not present on a smooth, sawn surface. The resulting cut, which follows that rough surface, will also be rough, attempting to conform the cut to all those irregularities in the surface.
Kenyon requires applying a lateral orienting pressure on the work piece. Kenyon moves the cant to orient it so that the fixed position saw blades cut along the curvature. In Kenyon, once the trailing edge of the cant has gone past the cant orientation means (the orienting pressure roller 6), the cant can no longer be shifted laterally to line up the saw blades with the curvature of the cant, so control is lost toward the end of the cut. This means that the end portion of the cut board frequently will not have the correct thickness and will have to be scrapped. Furthermore, the cant is moved laterally by the orienting pressure roller 6 which is also acting against the wany side of the cant, which results in a less accurate alignment of the cant relative to the saw blades and the relative to the curvature of the cant. Kenyon attempts to minimize this adverse effect (refer to FIG. 3) by having the point of contact of the orienting pressure roller 6a with the cant as close as possible to the edge(s) closest to the smooth (sawn) surface, and (refer to FIG. 5) by using more than one orienting pressure roller 6a, 6b and averaging the input from these multiple rollers.
In Kenyon, the sensor must be facing the concave side of the cant. The design will not work if the sensor 25 is facing the convex side of the cant, because the orienting pressure roller 6 can only push the cant away from the sensor 25; it cannot pull the board toward the sensor, as would be required to maintain a constant thickness if the sensor were on the convex side of the cant. Therefore, the cant must be properly oriented relative to the sensor 25 before the cant is fed to this prior art saw. This also means that a cant with a compound curvature (one which is concave in a portion of its length and convex in another portion of its length) cannot be adequately handled by the saw taught in Kenyon.